Cobalt is known to exist in a number of ores and minerals in various parts of the world. Cobalt minerals are commonly associated with minerals or ores of nickel, iron, silver, bismuth, copper, manganese, antimony, and zinc. Because cobalt and nickel are so similar, chemically, the separation of cobalt from the presence of nickel in ores (without also separating nickel from the ore) is a problem of long standing.
A convenient reference for information concerning the occurrence, chemistry, analysis, and processing of cobalt and its alloys may be found in the chapter titled "Cobalt and Cobalt Alloys", authored by F. Planinsek and John B. Newkirk, in pp. 481-494 of the KIRK-OTHMER ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Third Edition, Volume 6, published by John Wiley & Sons, Inc. 1979.
Hydrazine, N.sub.2 H.sub.2, is reported to be a strong reducing agent for many metals including V, Cr, Mn, Fe, Co, Ni, Cu, As, Se, Mo, Ru, Rh, Pd, Ag, Cd, Sn, Sb, Fe, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, Ce, U, Np, and Pu. For example, it is reported to reduce Fe.sub.2 O.sub.3 to Fe.sub.3 O.sub.4 and to reduce chromate ions, CrO.sub.4.sup.-- to Cr(OH).sub.3.
It has now been found that cobalt values, i.e. Co.sup.+3, in ores and minerals and the like may be selectively reduced and leached out, without substantial leaching of nickel values present in the ores and minerals. This is done by employing a reducing agent, e.g., hydrazine hydrosulfate, hydroxylamine, or sodium pyrosulfate, carried in an aqueous solution as a leaching agent. By this technique, efficient extraction of cobalt from the ores and minerals can be achieved without the expensive drying and roasting step which customarily precedes chemical extraction of the cobalt values, and without simultaneous extraction of substantial amounts of associated nickel values.